The fabrication of integrated circuit devices generally involves a variety of patterned layers of semiconductor, insulator and conductor materials. This patterning is often carried out by a process of forming one or more thin layers of material followed by removing unwanted portions of the layers. Such removal is generally carried out by exposing portions of the layers to a liquid, gaseous or ionic etching agent to remove the exposed portions of the layers. The nature and composition of the etching agent used to remove the exposed portions of the layers is dependent upon the nature of layer to be removed as well as the nature of the surrounding layers to be retained.
A photolithographic process is often used to define the desired pattern. In a photolithographic process, a photoresist layer is formed on the surface of the in-process device. The photoresist layer contains a photo-sensitive polymer whose ease of removal is altered upon exposure to light or other electromagnetic radiation. To define the pattern, the photoresist layer is selectively exposed to radiation and then developed to expose portions of the underlying layer to be removed. In practice, a mask is placed between the photoresist layer and a light source or other radiation source. The mask contains a pattern of opaque and transparent sections to selectively block or transmit the radiation. In a positive resist system, the portions of the photoresist layer exposed to the radiation are photosolubilized and the mask is designed to block the radiation from those portions of the photoresist layer that are to remain after developing. In a negative resist systems, the portions of the photoresist layer exposed to the radiation are photopolymerized and the mask is designed to block the radiation from those portions of the photoresist layer that are to be removed by developing. While other processes are possible, in general a pattern is formed to define portions of a material to remove, and portions of the material to retain.
Removal processes are often not complete. That is, after patterning a layer of material, some trace contamination, e.g., unremoved material, may remain on the underlying surface. Such trace contamination is often the result of trying to mitigate damage to the underlying or adjacent structures from the removal process itself by subjecting these surrounding structures to the removal process only for a limited time. For example, it may be experimentally or empirically determined that a particular time is needed to remove a particular thickness of metal. Ideally then, if the removal process is performed for the particular time, it would be expected that the particular thickness of that metal would be removed and damage to surrounding materials would be mitigated by not subjecting them to the removal process for an unnecessary amount of time. However, given the variabilities of typical manufacturing conditions, some of the metal intended for removal may remain on underlying structures.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for alternative methods for removal of metals from substrates.